1907.] Structural Constituents of the Nucleus, etc. 459 



Now such a correlation does sometimes occur in respect of a few characters, 

 but it becomes relatively insignificant when the total number of independent 

 pairs of allelomorphs is borne in mind. And if this causes difficulty in 

 dealing with relatively few characters, it obviously gathers in force when the 

 vast numbers of features which distinguish an organism are remembered. 



Eut if for the chromosomes we substitute the chromomeres as representing 

 the discrete units which are responsible for the production of the hereditary 

 characters, the last objection loses its force. The chromomeres, consisting of 

 special chromatin-containing linin bodies, are present in great quantities ; so 

 numerous that, as far as I am aware, they have never been counted in 

 a single chromosome. They fulfil the condition of being distinct entities ; 

 and also, at meiosis, the divergent chromosomes contain, or rather are made 

 up of, chromosomes arranged in two opposing groups, and derived from 

 different parents. 



At the same time, I am aware that there are certain difficulties introduced 

 by this suggested substitution of the chromomeres for the chromosomes, 

 though I think these are more apparent than real. 



The cardinal facts which we have to take into account are : first, the large 

 number of the allelomorphs and, secondly, their mutual independence. These 

 two circumstances, taken together, are irreconcilable with a view that would 

 regard the allelomorphs as invariably assigned to particular chromosomes. But 

 if we attach to the chromomeres, or to any other still smaller particles, the 

 properties of separate character-producing substances, the widely entertained 

 view as to the real structural persistence of the chromosomes themselves will 

 require some modification. For in order to give that complete independence 

 observed to exist between most of the allelomorphs, it is clear that any given 

 chromosome must be correspondingly indifferent as to which chromomeres 

 enter into its composition.* This, however, amounts to a surrender of the 

 doctrine that there exists any permanent structural arrangement in an 

 individual chromosome lasting from one generation to another. 



They might, perhaps, be compared with the hands that are successively 

 dealt out from a pack of cards : each new hand, in respect of the number of 

 cards, may resemble, but is not really identical with, those of the preceding 

 deals. So, too, the chromosomes which reappear at each division would be 

 similar to, but not necessarily the same as, those of the preceding division. 

 The material particles of which they are built up are shuffled in the intervals 



* In the heterotype pseudochromosomes, each member must, however, be composed of 

 homologous primordia contributed by the male and female parent respectively. It may 

 well be that this is the significance of synapsis, which forms so characteristic a feature of 

 the heterotype mitosis. 



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